The present invention relates to a magnetic disk drive. More specifically, the invention relates to a bearing mechanism for a carriage which supports a magnetic head for rotation, and a bearing mechanism for a spindle motor which supports a magnetic disk for rotation.
Conventionally, the magnetic disk drive (hereinafter referred to as HDD) includes a ball bearing that is disposed between a carriage hub and a rotational center shaft of the carriage hub. The carriage hub supports a magnetic head for magnetically recording and reproducing information on a magnetic disk. A ball bearing is also used between a rotating shaft of a spindle motor for rotating a magnetic disk and a fixed shaft. Two ball bearings are provided up and down of a rotating shaft in terms of the basic using method. For these ball bearing, an outer ring or an inner ring is rotated with a plurality of balls disposed between the inner ring and the outer ring. Each ball is held by a holder such that each space between the balls is made constant, and grease is filled between the balls and the inner and outer rings in order to provide smooth rotation. A shield is provided for covering a portion of the holder over the inner ring and outer ring so that the grease is not scattered.
Patent Document 1 (Japanese Patent Laid-Open No. 2000-105983) describes a technique of forming a lubricating oil film in a rolling bearing for a rotating shaft used in information apparatuses. In that disclosure, to reduce a variation in rotational torque at a low speed rotation generated due to stirring resistance of grease or lubricating oil, ester lubricating oil whose dynamic viscosity at 40° C. is 25 to 150 mm2/s is dropped on the frictional surface of the rolling bearing, or the surface is subjected to oil plating to form a lubricating oil film.